(1) Field of the Invention
This invention relates to a porous scaffold having pores for seeding cells, a method of producing the same, and a method of using the porous scaffold. More specifically, this invention relates to a porous scaffold usable for seeding cells capable of differentiation and organization to form living tissues and organs such as bone, cartilage, ligament, skin, blood vessel, pancreas, and liver that are injured or lost due to disease, accident, and the like for the purpose of repairing the injured or lost tissues and organs, a method of producing the same, and a method of using the porous scaffold.
(2) Description of Related Art
As conventional methods for repairing and treating living tissues and organs such as cartilage, skin, bone, ligament, skin, blood vessel, pancreas, and liver that are injured or lost due to disease, accident, and the like, treatment methods by an artificial organ, organ transplantation, and the like have been known. However, in the case of the artificial organ, there are problems such as insufficient function, wearing, loosening, and breakage due to artificial member, and the like. Also, in the case of the organ transplantation, there is the problem of donor shortage, and, in the case where the donor is an unrelated person, rejection response clue to immunologic response is in question.
Due to the various problems, a treatment method by tissue engineering is considered to be ideal, and studies for regenerating a tissue to be transplanted by culturing cells of a patient in a porous scaffold are being actively conducted. As specific examples, firstly, a method wherein living cells are proliferated ex vivo and seeded in a porous scaffold that is used as a scaffold for the living cells or tissue for ex vivo culture, and the thus-formed living tissue is transplanted to the living body is known. Secondly, a method wherein living cells are seeded in a porous scaffold to be implanted into a living body for inducing regeneration of a living tissue in vivo is known. Thirdly, a method wherein a porous scaffold is directly implanted into an injured site to induce neighboring cells to enter the porous scaffold for inducing formation of a new tissue is known. Thus, the porous scaffold for inducing and promoting formation of living tissue and maintaining the shape of the living tissue has the remarkably important role. The porous scaffold is required to have biocompatibility as a property of not influencing on living bodies, bioabsorbability for allowing formation of new living tissue and capable of degradation and absorption, an appropriate mechanical strength, and the like.
As such scaffolds, porous materials of bioabsorbable polymers such as polylactic acid (PLA), polyglycolic acid (PGA), a copolymer of lactic acid and glycolic acid (PLGA), collagen, and the like have commonly been used in the art (see JP-A-2003-10309).
In the case of culturing cells by using the porous scafold of bioabsorbable polymer, the cells are seeded and adhered to the material. However, the number of cells to be collected from a patient is limited, and, in view of the fact that it is most desirable to seed and adhere all of the obtained valuable cells to the porous scaffold, it is remarkably important to seed and adhere any type of cells to the porous scaffold irrespective of easily-adherable cells and hardly-adherable cells.
However, in the case of seeding cells in the porous material of bioabsorbable polymer, cell leakage from a periphery of the porous material is violent, and it is difficult to seed cells at a high efficiency to porous scaffold having a low porosity. Further, in the case of hardly-adherable cells, almost all of the cells cannot adhere to the material to adversely affect on the regeneration of tissue and organ.
Osteoarthritis deformans is a disease frequently seen in the field of orthopedics and often involves severe dysfunction. Though prosthetic joint surgery is the mainstream of surgical treatment, currently available prosthetic joint parts made from metals and high molecular polymers have the above-described problems of infection, wearing, loosening, and breakage. In the case of tissue transplantation, there are problems of donor shortage and rejection reaction based on immunological response, too. Due to existence of the various problems, the treatment methods by the approach of tissue engineering is now considered to be ideal, and studies on regeneration of cartilage tissue are being actively conducted.
In order to regenerate a cartilage tissue by the approach of tissue engineering, a three-dimensional porous scaffold is required as a scaffold for chondrocytes or stem cells differentiatable into chondrocytes to proliferate and a support for a living tissue being formed.
However, since a central part and a surface layer of a conventional porous scaffold have almost identical porous structures, seeded cells do not stay in the porous scaffold, and a large part of the cells passes through openings and slits that are larger than the size of the cell to leak from a periphery of the porous scaffold. Accordingly, it is remarkably difficult to efficiently seed the chondrocytes or the stem cells differentiatable into chondrocytes in the culturing porous scaffold, and, therefore, it is impossible to obtain an effective cell seeding efficiency and to accumulate the cells in the culturing porous scaffold by a large scale, thereby adversely affecting on the cartilage tissue regeneration.
Also, since neighboring different tissues have been regenerated in identical porous scaffold, such environment is different from the neighboring structure in a living tissue or organ where different tissues are combined and multilayered. Also, in order to simultaneously regenerate neighboring tissues, it is desirable to use a porous scaffold having materials and structures suitable for regenerating both of the tissues.